Motorized devices for opening and closing sectional overhead doors have long been known in the art. These powered door operators were developed in part due to extremely large, heavy commercial doors for industrial buildings, warehouses, and the like where opening and closing of the doors essentially mandates power assistance. Later, homeowners' demands for the convenience and safety of door operators resulted in an extremely large market for powered door operators for residential usage.
The vast majority of motorized operators for residential garage doors employ a trolley-type system that applies force to a section of the door or barrier for powering it between the open and closed positions. Another type of motorized operator is known as a “jack-shaft” operator, which is used virtually exclusively in commercial applications and is so named by virtue of similarities with transmission devices where the power or drive shaft is parallel to the driven shaft, with the transfer of power occurring mechanically, as by gears, belts, or chains between the drive shaft and a driven shaft, normally part of the door counterbalance system, controlling door position. While some efforts have been made to configure hydraulically or pneumatically-driven operators, such efforts have not achieved any substantial extent of commercial acceptance.
The well-known trolley-type door operators are attached to the ceiling and connected directly to a top section of a garage door and for universal application may be powered to operate doors of vastly different size and weight, even with little or no assistance from a counterbalance system for the door. Since the operating force capability of trolley-type operators is normally very high, force adjustments are normally necessary and provided to allow for varying conditions and to allow the operator to be adjusted for reversing force sensitivity, depending on the application. When a garage door and trolley-type operator are initially installed and both adjusted for optimum performance, the overhead door system can perform well as designed. However, as the system ages, additional friction develops in door and operator components due to loss of lubrication at rollers and hinges. Also, the door can absorb moisture and become heavier, and counterbalance springs can lose some of their original torsional force. These and similar factors can significantly alter the operating characteristics seen by the operator, which may produce erratic door operation such as stops and reversals of the door at unprogrammed locations in the operating cycle.
One system that addresses the aforementioned problems is disclosed in U.S. patent application Ser. No. 11/165,138 filed on Jun. 22, 2005, which is incorporated herein by reference. Such a system is referred to as a pivoting and barrier locking operator system. Briefly, such a system includes a motor with appropriate gearing that is linked to a counterbalance system that assists in moving a barrier, such as a sectional door, between defined limit positions. The motor either directly rotates a counterbalance drive tube or imparts rotational forces to a drive assembly which in turn rotates a counterbalance drive tube. Typically, the drive assembly is used when the operator system is installed for use with a pre-existing counterbalance system. In either version of operator system, the drive tube is connected at each end to a cable storage drum. Lift cables are secured at one end to each storage drum and at respective ends to at least a bottom section of the barrier. Accordingly, as the drive tube is rotated, the storage drums pay-out or reel in the respective cable.
With most cable storage drums, whether used in winches or in counterbalance systems for barriers, the drums positioned on shafts are rotatable about the axis of the shaft and are either fixed to the shaft such that the drum and shaft revolves together or the shaft is non-rotatable and serves as support and a bearing surface for the drum. Some prior art has drive gear systems where a drive gear, with input from a torque source, drives the driven gear ring attached or formed into the outer perimeter of the cable storage drum. In these prior art devices the rotation of the cable drum's driven gear is in the opposite direction of the drive gear. Where in most applications this opposite rotation is acceptable, in counterbalancing systems, such as disclosed in the '138 application referenced above, it is not. Known designs that will allow the drive and driven gears to rotate the same direction require an idler gear that is driven by the drive gear and which then drives the driven gear. This arrangement requires additional room and bracketry to mount and contain the idler gear.